Starting from version 4.0 there are 3 types of image which you can select when creating a new backup – full, incremental and differential.
Full backup includes all data and is similar to previous images (but the image file format has been changed). Incremental and differential are based on the previous image and include only data changed since the last backup.
A previous image is called a base image and can be a full backup, or another incremental image. If for a particular block there's no difference between the current state and the base image, data is not written into the current image, but a reference to a base image is placed instead.
The base image and all subsequent incremental images have the same partitions backed up. The create wizard dialog for incremental image shows the partitions selected for information purposes only; it does not allow you to change the selection. If it appears that the partition included into base image is no longer available or reformatted, a warning will be shown and the image creation stopped.
A password, if one exists, is shared between all images and cannot be changed in an incremental image. All other options like compression, file splitting, and description are individual for every image.
Normally incremental images are named by the date/time of creation and located in the folder below the full backup, so the file structure will be as follows:
<Images location>\<Full backup> <Images location>\<Full backup>\<Incremental 1> <Images location>\<Full backup>\<Incremental 2>
When you select any image as a base for incremental image, the application scans the parent folder and sibling folders (if it is not a full backup) or children folders (for full backup selected).
All found images are enumerated and shown as a list from which user can select a required base image. If more than one image with the same sequence exists, it will be ignored. For example, the full backup has sequence #0, the first incremental image will have sequence #1. If another incremental image is created based on #0, it will become #1 again, so one of them will be ignored during the enumeration.
When an incremental image is selected for restoring, all sequence images starting from the full backup and including the selected image must be present in the folders as described above.
Backward image compatibility is supported but forward is not. All new images created will have new image format.